Study finds aspirin not always a heart aid

More than 20 million Americans take aspirin regularly to help prevent heart attacks and strokes. But new evidence suggests that for many of them, the pills do little if any good.

Recent studies have found that anywhere from 5 percent to more than 40 percent of aspirin users are "non-responsive" or "resistant" to the medicine. That means that aspirin does not inhibit their blood from clotting, as it is supposed to.

"They are taking it for stroke and heart attack prevention, and it's not going to work," said Dr. Daniel Simon, associate director of interventional cardiology at Brigham and Women's Hospital in Boston and an associate professor at Harvard.

Most physicians don't test patients for aspirin resistance. Several doctors said that even resistant patients probably would still be better off taking aspirin than not doing so.

Also, people who use aspirin to fight pain or inflammation are not affected by the new findings.

Scientists are racing to clarify further the significance of aspirin resistance and the way to counteract it. What they learn could influence how one of the oldest and most widely consumed medicines is used, perhaps leading to more customized therapies.

"You're talking about a huge number of people" who might not be benefiting, said Dr. Michael Domanski, head of the clinical trials unit of the National Heart, Lung and Blood Institute.

Although some experts have known about aspirin resistance for years, it is a topic of growing interest as studies have confirmed that aspirin takers who are resistant have a higher rate of heart attacks and strokes than non-resistant aspirin users.

"Aspirin resistance is associated with a worse outcome," said Dr. Deepak Bhatt, director of the interventional cardiology fellowship program at the Cleveland Clinic.

New tests make it far easier than in the past to measure response to aspirin. Companies selling such tests are calling attention to aspirin resistance to help in their marketing.

Some experts caution that not enough is understood about the meaning of resistance to justify routine tests. Moreover, the experts say, it is unclear what to do for aspirin-resistant patients.

"For none of these tests is there evidence that altering treatment is beneficial to the patient," said Dr. Alan Michelson, director of the center for platelet function studies at the University of Massachusetts. "I don't think doctors should do these tests, and I don't think they should change treatments based on these tests."

A small but growing number of doctors are starting to test patients.

They argue that even without conclusive evidence it is reasonable to alter therapy rather than have a patient continue to take a drug that a test shows is ineffective.